A wide variety of cooking methods and cooking devices have been provided in the past. Deep fat frying and broiling are illustrative of methods of cooking that have been around for years. The conventional oven is also illustrative of cooking devices that have been in use for many years. In fact, simple ovens in various forms have been in use for centuries in homes, commercial bakeries, institutional kitchens and restaurants.
Conventional ovens have been provided in a variety of models and sizes, for example, a permanent, built-in style, mounted in cabinetry, together with or independent of a stove top unit. Conventional ovens have also been provided of a portable design. While the conventional oven remains a basic essential cooking unit in the home as well as restaurants or the like, conventional ovens do have their shortcomings. Conventional ovens, for example, tend to cook slowly and thus consume a good deal of the user's time.
Attempts have been made to overcome this problem; for example, microwave ovens have become popular. While microwave ovens cook rapidly, they too have their shortcomings. For example, it is difficult to brown food in a microwave oven.
Other attempts at solving the slowness of conventional ovens have been to include a circulating fan to move the air in the oven. While such circulating fans have provided more rapid cooking, the time required is still very substantial. Such existing ovens perform their tasks in a similar way. The majority of such cooking devices consist of a rectangular oven, usually equipped with a plurality of racks, much like that found in conventional in-home ovens. Often at the rear of the oven is a squirrel-cage type blower which draws the air through a hole in the interior rear wall and blows the air out to the sides where it is directed to perforations in the two interior side walls. This pressurized air is then forced through the perforations toward the rear center of the oven enclosure, where it is drawn into the blower intake hole and recirculated, thereby completing a closed loop. An oven produced by Rair follows the above pattern with the exception of circulating the air through a cylindrical chamber with its axis positioned horizontally.
Air velocities within the cooking chamber of such ovens are low in comparison to the present method and vary widely within each oven. The velocities are generally the highest immediately in front of the blower intake. A typical average air speed found in a commercial restaurant convection oven is approximately 350 feet per minute.
A conventional square or rectangular chamber, especially with sharp corners, offers great resistance to the smooth flow of air due to the abrupt change in direction of the air stream at each corner encountered. This makes it difficult for conventional ovens to achieve the air velocities of the present invention. Turbulence is created in conventional chambers as well as stagnant areas of relatively cool air in the corners and thus the air velocities are difficult to obtain without displacement of the food pieces. Earlier forced air designs make use of large blowers and powerful motors to pressurize the air and force it as evenly as possible through the cooking chamber, usually through perforations or louvers in the interior walls of the cooking chamber. Such prior devices have not been effective to produce the results found in the present invention since they do not achieve the necessary velocities. Also such high power devices are not practical when designing a lightweight portable appliance, due to the excessive noise, added cost and space requirements of such a design.
Prior ovens with fans have not been able to get their fans to achieve high rates of speed for the two following reasons. Ovens with fans often disrupt or restrict their air flow in one or both of two ways:
The prior ovens disrupt or restrict the fans air output by forcing the air through a grease filter. The function of that filter is typically to protect the fan from grease. The present fan is self-cleaning and does not have the problem of having to restrict air velocities by forcing the air through a grease filter. PA1 Prior ovens also disrupt or restrict the air flow by placing the heating elements so that the air coming off the fan blades passes over and around the heating element. This is done to heat the air, but it also severely disrupts the air flow making it more difficult to achieve higher, free-flow air velocities. The present invention disposes the heating element behind the fan in a position where it does not disrupt or restrict the air flow, thus achieving higher rates of air flow with better results.
Prior ovens with fans do not extend the fans down into the cooking chamber. The fans are generally recessed into the wall of the cooking chamber or into the roof of that cooking chamber. The fans are therefore covered by or partially blocked by either the wall, a filter, of some other enclosure or housing.
The fan blade in the present invention projects into the cooking chamber where it drives the air free and essentially unrestricted by any enclosure. It is the position of the present fan within or relative to the chamber that contributes to its ability to achieve the high air velocities and the attendant results.
Various means of heating the air are used, usually employing natural gas heat exchangers located in the sides of the oven or electrical tubular heating elements located in the lower portion of the oven.
A rapid cooking device has been the deep fat fryer. Such fryers are typically used to prepare French fries, breaded shrimp, fried chicken and the like. Deep fat fryers will typically cook food pieces in from one to five minutes. Deep fat fryers brown the product and develop desirable flavor characteristics. Deep fat fryers, however, also have inherent disadvantages. One such inherent disadvantage is the fact that the cooked food product has very high levels of fats, thus increasing the caloric content as well as the potential adverse effects of cholesterol on the consumer's circulatory system.